A process for preparing aluminum base alloys

ABSTRACT

A process for preparing aluminum base alloys containing silicon and magnesium comprising the steps of hot working, quenching and aging and to improved hot-worked aluminum-based alloys having high-strength and high-impact properties.

0 United States Patent [151 3,642,542 Sperry et a1. Feb. 15, 1972 [54]PROCESS FOR PREPARING [56] References Cited ALUMINUM BASE ALLOYS UNITEDSTATES PATENTS l t il [72] 2,65,: v 3,113,052 12/1963 Schneck ..14s/11.s3,234,054 2/1966 Sperry 148/1 1.5 [73] Assignee: Olin CorporationPrimary Examiner-Richard 0. Dean [22] 1970 AttorneyRobert H. Bachman andGordon G. Menzies [21] App1.No.: 14,189

ABSTRACT U.S. A process for preparing aluminum base alloys containing 5.75/146, 75/147, 148/325 icon and magnesium comprising the steps of hotworking, [5 Cl- ..C22f quenching and aging and to improved hot.workedaluminum- [58] Field of Search ..75/ 146, 147, 141, 142; based ll h ihigh-strength and high-impact properties.

1 1 Claims, No Drawings PROCESS FOR PREPARING ALUMINUM BASE ALLOYS Thepresent invention relates to a process for obtaining an aluminum basealloy containing silicon and magnesium. The present invention alsorelates to an improved aluminum base alloy containing silicon andmagnesium, wherein said alloy is a hotworked alloy and has high-strengthand high-impact properties.

Hot-worked aluminum base alloys containing magnesium and silicon findwide application in a wide variety of uses, for example. they may bereadily used as extrusions, forgings or rolled products.

There are many applications where it is highly desirable to develop ahot-worked product having a combination of highstrength and high-impactproperties. For example, there are certain applications for aluminumalloy extrusions where high impact strength is one of the majorrequirements. A highway bridge railing or median barrier of extrudedaluminum must absorb a considerable amount of energy from a vehiclecrashing into it before it fails.

Accordingly, it is a principal object of the present invention toprovide new and improved hot-worked aluminum base alloys.

It is a further object of the present invention to provide a process forobtaining improved hot-worked aluminum base alloys.

It is a still further object of the present invention to provideimproved hot-worked aluminum base alloys having a combination ofhigh-strength and high-impact properties.

Further objects and advantages of the present invention will appearhereinafter.

In accordance with the present invention it has now been found that theforegoing objects and advantages may be readily obtained.

The improved hot-worked alloy of the present invention consistsessentially of silicon from 0.3 to' 1.3 percent, magnesium from 0.3 to1.5 percent, chromium from 0.03 to 0.40 percent and zirconium from 0.03to 0.20 percent. Preferably, the alloy of the present invention alsocontains manganese in an amount from 0.03 to 0.4 percent.

The improved alloy of the present invention is a hot-worked product andhas a surprising combination of high-strength and high-impactproperties. The microstructure of the alloy of the present invention ischaracterized by a substantially unrecrystallized grain structure. lt issurprising that the combination of ingredients of the alloy of thepresent invention achieves such excellent properties and it is furthersurprising that the substantially unrecrystallized grain structureresults in improved impact properties.

The process of the present invention comprises: hot working the alloysat a finishing temperature in excess of 850 F.; water quenching thealloysdown to a temperature of 350 F. or below at a cooling rate of from1,000 to 10,000 F. per minute; and thermally artificially aging thealloys at a temperature from 200 to 410 F. for from 15 minutes to 24hours.

As stated hereinabove, the alloys of the present invention arecharacterized by a surprising combination of high-strength andhigh-impact toughness. For example, generally the minimum propertiesobtained in accordance with the foregoing process are as follows:tensile strength at least 38,000 p.s.i.; yield strength at 0.2 percentoffset at least 35,000 p.s.i. and elongation at least 8 percent.

The minimum impact toughness of the alloys of the present invention isfor a xi-inch-thiclt specimen the Charpy Notch impact test yields atleast 15 foot pounds. One would obtain at least 20 foot-pounds for a0.394-inch-thick specimen, and typically 30 to 40 foot-pounds.

In addition to the foregoing the alloy of the present invention hasnumerous other highly desirable characteristics, for example, it iseasily extruded and has good corrosion resistance.

The alloy of the present invention contains from 0.3 to 1.3 percentsilicon and preferably from 0.4 to 0.9 percent silicon.

Silicon in the preferred range has been found to give particularlyadvantageous results. The alloy of the present invention containsmagnesium in an amount from 0.3 to 1.5 percent and preferably from 0.4to 1.0 percent. The chromium content may vary from 0.03 to 0.40 percentand preferably from 0.05 to 0.35 percent. The zirconium may vary from0.03 to 0.20 percent and preferably from 0.05 to 0.15 percent.

As stated hereinabove, it has been found to be particularly advantageousto include manganese in an amount from 0.03 to 0.4 percent andpreferably in an amount from 0.05 to 0.3 percent.

Other especially advantageous additives are titanium up to 0.10 percentand vanadium up to 0.15 percent.

Naturally, the present invention contemplates conventional impuritiescommon for alloys of this type. This is important since it indicatesthat the improved properties of the alloys of the present invention areobtainable with normal commercial purity materials. For example, normalimpurities include 0.60 percent maximum iron; 0.30 percent maximumcopper; 0.50 percent maximum zinc; up to 0.008 percent boron; 0.10percent maximum each of other elements the total of which is a maximumof 0.50 percent.

The manner of melting and casting the alloy is not especially criticaland conventional methods of melting and casting may be convenientlyemployed. It is desirable to uniformly distribute the silicon andmagnesium throughout the matrix of the alloy before the process of thepresent invention is performed, such as by a homogenization heattreatment subsequent to the casting operation. Before or during hotworking some high temperature precipitate should be formed due to Cr, Zrand Mn, as this is the mechanism by which recrystallization isinhibited. However, this can be accomplished by reheating for hotworking as well as by homogenization.

After casting the alloy is hot worked at a finishing temperature inexcess of 850 F. and preferably in excess of 900 F for example, forging,rolling or extruding. By inishing temperature it is meant the finaltemperature at which significant deformation is obtained in thehot-working operation. When the alloy is extruded, the die exittemperature should be in excessof 850 F. It is preferable that theactual temperature be high enough to dissolve substantially all Mg andSi which is available for maximum strengthening.

Following the hot working operation it is important to rapidly quenchthe material to a temperature of at least 350 F. at a cooling rate of1,000 to 10,000 F. per minute. The rapid quenching is normally obtainedby plunging the material in water or by passing the material through awater spray quench.

Optionally, the material may then be cold worked up to 5 percent, e.g.,rolling, stretching, etc.

The material should be then artificially aged at a temperature of 200 to410 F. for 15 minutes to 24 hours.

The alloys of the present invention are quench sensitive. It is aparticularly surprising finding of the present invention that thisquench sensitivity can be controlled with respect to a particularlypreferred composition. This is accomplished by a critical adjustment ofthe quantities of chromium, zirconium and manganese present in the alloyso that each of these materials are present in an amount of 0.03 to 0.2percent, and the total chromium plus zirconium plus manganese content isfrom 0.2 to 0.35 percent. It has been found that when the compositionhas been controlled in this manner, the alloy can be air cooled at acooling rate from to 1,000 F. per minute; otherwise, the alloy must bewater quenched at the more rapid rate specified hereinabove.

The air cooling is nonnally achieved by using appropriately placed fans.

In this particularly preferred composition, the hot working step shouldbe performed at a finishing temperature in excess of 900 F. andpreferably in excess of 950 F.

As stated hereinabove, the alloy of the present invention is ahot-worked product with a surprising combination of highstrength andhigh-impact properties and with a microstructure characterized by asubstantially unrecrystallized grain structure.

The process of the present invention and improvements resultingtherefrom will be more readily apparent from a consideration of thefollowing illustrative examples.

EXAMPLE 1 lngots were prepared by direct chill (DC) casting in aconventional manner summarized as follows. Melting and alloying e impacttest value TABLE II Charpy Section Y.S. Elongation impact thicknessQuench UIS (K 5,1.) (percent strength (lnehes) Alloy method (K s.1.) at0.2% in 2 1n.) (IL-lbs.) 43. 5 41. 10 20. 1% A 4 .1 11 23.2 4 .5 9. 9. 5.8 54 B 42.5 42. 4 32.3

4 0 39. 8 A 46.0 43.1 9.5 27.8 V B 41. 3 36.5 9. 5 35. 2 A 45.8 g3. o 0.5 41. 4 7. 0 0. l5 A 44.0 41.0 11.5 68.0 B 38.6 33. 3 12 e0. 5 2 48. 646. 0 l2. 5 4 5 was carried out in a gas-fired, open hearth furnace.After al- EXAMPLE lll loying the melt was degassed by gaseous chlorinefluxing for 20 minutes. The average pouring temperature was l,370 F. Theaverage casting speed was 4% inches per minute and the metal head wasmaintained between 2% and 3 inches. The composition of the alloysprepared are given in Table I below.

TABLE 1 Alloy A silicon 0.78 magnesium 0A7 iron 0.14 titanium 0.01chromium 0.050 zirconium 0.056 manganese 0.054 copper 0.00 zinc 0.04aluminum Balance Alloy B silicon 0.81 magnesium 0.53 iron 0.14 titanium0.01 chromium 0.107 zirconium 0.108 manganese 0.108 coppcr 0.00 zinc0.03 aluminum Balance EXAMPLE II The alloys prepared in Example 1 wereprocessed in the following manner. The ingots were given ahomogenization heat treatment of about l,025 F. for about 10 hoursfollowed by cooling in air. The billets were sawed to length andreheated for extrusion in a gas-fired, control temperature set at l,000F. Measured surface temperatures ranged between 975 and 1,025 F. beforeentering the press. Three extrusion dies were used to produce sectionthicknesses of one-eighth, one-fourth, and one-half inch. Exittemperatures ranged from 980 to 1,000" F. One extrusion of eachthickness was fan cooled as it exited from the press at a cooling ratein the range of the process of the present invention; another was waterquenched by passing it through an open ended trough fed by an upwardflow of water at both ends at a cooling rate in the range of the processof the present invention. All extrusions were aged at room temperaturefor about 24 hours, followed by artificial aging at 350 F. for 5 hours.Tensile test specimens and Charpy impact specimens were taken from theextrusions. The and Va-lnCh-thiCk extrusions were tested with reducedingots were prepared in a conventional manner from two kilogram meltscast by the tilt mold (Durville) process. The resultant compositions areindicated in Table 111 below.

TABLE 111 Alloy C silicon 0.71% magnesium 0.56% iron 0.16% copper 0.01%titanium 0.02% zirconium 0.16% aluminum Balance Alloy D silicon 0.83%magnesium 0.58% iron 0.20% copper 0.0l% titanium 0.01% chromium 0.31%aluminum Balance Alloy E silicon 0.71% magnesium 0.57% iron 0.16% copper0.0l% titanium 0.02% chromium 0.22% zirconium 0.10% aluminum BalanceAlloy F silicon 0.78% magnesium 0.58% iron 0.17% copper 0.01% titanium0.02% chromium 0.10% manganese 0.09% zirconium 0.11% aluminum BalanceEXAMPLE IV The alloys prepared in Example 111 were processed in thefollowing manner. The ingots were homogenized at 1,025 F.

for 12 hours. The ingots were hot rolled from 1,000 E, percent in onepass. The materials were quenched by plunging into water at roomtemperature, thus providing a cooling rate in the range of the processof the present invention. The materials were age hardened 5 hours at 350F. The materials TABLE IV Charpy impact Tensile properties (KL-lbs.)

Ultimate Yield Elongation Alloy (K s.i.) (K s.i.) (percent) IndividualAverage 43. 7 38.6 14 10.4,11.8 11.1 C 44. 1 38. 4 13 12. 6, 14. 3 13. 543. 3 38. 2 11 9. 90, 10. 7 10.3 1) 44. 3 39. 7 11 141,147 14. 4 43. 538. 4 13. 5 20. 5, 22. 4 21. 5 E 45. 2 39. 3 12. 18. 6,17.3 18.0 45. 239. 9 12. 5 18. 0, 17. 8 17. 9 F 47.2 42.3 11.5 104,189 19.2

EXAMPLE V lngots were prepared in a manner after Example 1 to have thecomposition indicated in Table V below.

Alloy (Commercial Alloy AA 635 I) silicon 1.08% magnesium 0.65% iron0.19% copper 0.004% titanium 0.024% manganese 0.66% boron 0.004%

Alloy J (Commercial Alloy 6061) silicon 0.64% magnesium 1.10% iron 0.25%copper 0.25% titanium 0.017% chromium 0.18% manganese 0.053%

EXAMPLE V1 The materials from Example V were processed in a manner afterExample 1V except that the materials were hot rolled 50 percent in onepass rather than 80 percent and Alloys I and J were aged for 8 hours at350 F. The results are given in Table VI below and clearly show thesurprising propertiesotiAlloy H not contain the chromium addition whichrepresents the alloy of the present invention. it should be noted thatthe Charpy impact test utilized standard 0.394 inch specimens.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated b the appended claims. and all changes which come withint e meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

l. The process for preparing a material having a combination ofhigh-strength and high-impact properties which comprises: providing analuminum base alloy consisting essentially of from 0.3 to 1.3 percentsilicon, 0.3 to 1.5 percent magnesium, 0.03 to 0.4 percent chromium,0.03 to 0.2 percent zirconium, balance essentially aluminum; hot workingsaid alloy at a finishing temperature in excess of 850 F.; waterquenching said alloy to a temperature of at least 350 F. at a coolingrate of from l,000 to 10,000 F. per minute; and thermally artificiallyaging said alloy at a temperature of from 200 to 410 F. for 15 minutesto 24 hours.

2. A process according to claim 1 wherein said alloy contains manganesein an amount from 0.03 to 0.4 percent.

3. A process according to claim 1 wherein said hot working is extrudingat a die exit temperature in excess of 900 F.

4. A process according to claim 1 wherein said hot working is rolling ata finishing temperature in excess of 900 F.

5. A process according to claim 1 wherein the alloy is homogenized priorto hot working.

6. A process according to claim 1 wherein after said water quenchingstep said alloy is cold worked up to 5 percent.

7. The process for preparing a material having a combination ofhigh-strength and high-impact properties which comprises: providing analuminum base alloy consisting essentially of silicon from 0.3 to 1.3percent, magnesium from 0.3 to 1.5 percent, chromium from 0.03 to 0.2percent, zirconium from 0.03 to 0.2 percent, manganese from 0.03 to 0.2percent, balance essentially aluminum, wherein the total chromium pluszirconium plus manganese content is from 0.2 to 0.35 percent; hotworking said alloy at a finishing temperature in excess of 900 F; aircooling said alloy to a temperature of at least 350 F. at a cooling rateof from to l,000 F. per minute; and thermally artificially aging saidalloy at a temperature offrom 200 to 410 F. for 15 minutes to 24 hours.

8. A process according to claim 7 wherein said hot working is extrudingat a die exit temperature in excess of 950 F.

9. A process according to claim 7 wherein said hot working is rolling ata finishing temperature in excess of 950 F.

10. A process according to claim 7 wherein the alloy is homogenizedprior to hot working.

11. A process according to claim 7 wherein after said air cooling stepthe alloy is cold worked up to 5 percent.

2. A process according to claim 1 wherein said alloy contains manganesein an amount from 0.03 to 0.4 percent.
 3. A process according to claim 1wherein said hot working is extruding at a die exit temperature inexcess of 900* F.
 4. A process according to claim 1 wherein said hotworking is rolling at a finishing temperature in excess of 900* F.
 5. Aprocess according to claim 1 wherein the alloy is homogenized prior tohot working.
 6. A process according to claim 1 wherein after said waterquenching step said alloy is cold worked up to 5 percent.
 7. The processfor preparing a material having a combination of high-strength andhigh-impact properties which comprises: providing an aluminum base alloyconsisting essentially of silicon from 0.3 to 1.3 percent, magnesiumfrom 0.3 to 1.5 percent, chromium from 0.03 to 0.2 percent, zirconiumfrom 0.03 to 0.2 percent, manganese from 0.03 to 0.2 percent, balanceessentially aluminum, wherein the total chromium plus zirconium plusmanganese content is from 0.2 to 0.35 percent; hot working said alloy ata finishing temperature in excess of 900* F.; air cooling said alloy toa temperature of at least 350* F. at a cooling rate of from 100* to1,000* F. per minute; and thermally artificially aging said alloy at atemperature of from 200* to 410* F. for 15 minutes to 24 hours.
 8. Aprocess according to claim 7 wherein said hot working is extruding at adie exit temperature in excess of 950* F.
 9. A process according toclaim 7 wherein said hot working is rolling at a finishing temperaturein excess of 950* F.
 10. A process according to claim 7 wherein thealloy is homogenized prior to hot working.
 11. A process according toclaim 7 wherein after said air cooling step the alloy is cold worked upto 5 percent.